We worked in a sewage treatment plant and take care of their plc work. They have an issue with noise some of the analog signals in the plant. When the vfds on their blowers start, some of their tank levels and D.O. level feedback signals just go really hay-wire. Jump all around and trigger false alarms etc.
All the analog wiring is shielded and grounded. The wiring to the blower motors is all in EMT conduit that doesn't even go close to the EMT conduit where the signals come in from the tanks. The vfds and motors all have ground wires. It is only 5 analog signals that this happens on. All the rest are okay.
Incidentally, all 5 of these are on the same AI card, but the card is pretty new.
I am not a specialist in noise like this, but I checked for a few things I thought could be obvious, but I didn't find anything. Except whoever installed the blower vfds ran both the line and load wiring of the drives in the same conduit for about 10' to a junction box where they split out.
Could this cause such as issue??
Is there a possibility the ground wires are not connected to earth so it has no way to "drain" the system??
Where would you start for something like this??
All the analog wiring is shielded and grounded. The wiring to the blower motors is all in EMT conduit that doesn't even go close to the EMT conduit where the signals come in from the tanks. The vfds and motors all have ground wires. It is only 5 analog signals that this happens on. All the rest are okay.
Incidentally, all 5 of these are on the same AI card, but the card is pretty new.
I am not a specialist in noise like this, but I checked for a few things I thought could be obvious, but I didn't find anything. Except whoever installed the blower vfds ran both the line and load wiring of the drives in the same conduit for about 10' to a junction box where they split out.
Could this cause such as issue??
Is there a possibility the ground wires are not connected to earth so it has no way to "drain" the system??
Where would you start for something like this??